Broad use of hydrogen as a fuel or energy carrier will provide better energy security, return major economic, environmental, and health benefits, and help minimize climate-change impact of greenhouse-gas emissions from energy use. Hydrogen couples into any realistic model of “sustainable carbon-hydrogen-electricity cycles” in an integrated and critical manner.
For storage and delivery, liquid hydrogen (LH2) is the superior choice rather than compressed (CH2), adsorbed, or chemical compounds of hydrogen because of LH2's higher volumetric energy density and gravimetric energy density compared to other hydrogen storage methods. The ratio of the ideal minimum work input per unit mass of gas to the real work input per unit mass of gas for a practical liquefier is called figure of merit (FOM). Currently the majority of gaseous hydrogen (GH2) is liquefied using liquid nitrogen pre-cooled Claude-cycle plants. These conventional large-scale liquefiers are limited to a FOM of ˜0.35. Small-scale conventional liquefiers seldom achieve FOMs of 0.25. Such a low FOM increases operating costs of hydrogen liquefiers and thereby the price of dispensed LH2 or CH2 fuel.
A relatively small number of hydrogen liquefiers presently exist in the world. Most of them are large industrial plants with capacities ranging from ˜5 metric tons/day to ˜100 metric tons/day. The majority of commercial H2 has been used for non-transportation applications such as at refineries and ammonia fertilizer plants. Few commercial liquefaction facilities have been built with capacities below ˜5 metric tons/day because the installed costs tend to increase sharply on a per metric ton/day basis as the capacity decreases. The depreciation of high capital costs of hydrogen liquefiers increases the price of dispensed LH2 or CH2 fuel. For example, a 1 metric ton/day LH2 facility has an approximate installed cost of ˜$9-11 million, i.e., ˜$10 million/metric ton/day. Over a 20-year operating period of a plant of this capacity and cost, straight-line depreciation gives a contribution of ˜$1.45/kg H2 to fuel cost.
The major barriers to deployment of fuel-cell electric vehicles are lack of local supply and refueling infrastructure with capacity in the range of 0.1 to 1 metric ton/day at each refueling station with delivery of LH2 or CH2 at the same price or less than gasoline on a fuel cost/mile driven basis. Cost-effective and efficient hydrogen liquefiers on this scale for such refueling supply and refueling stations do not exist. These two key barriers to rapid adoption of hydrogen fuels can be eliminated by development of highly-efficient and low-cost small-scale liquefiers.